Modified polytetrafluoroethylene resins and blends thereof

ABSTRACT

Dispersion-process-produced, non-melt-processible, particulate, core-shell, tetrafluoroethylene copolymer comprising recurring units of tetrafluoroethylene and modifying recurring units of at least one ethylenically unsaturated comonomer that is copolymerizable with the tetrafluoroethylene, the number of recurring units of comonomer in the shell being sufficient to enable the copolymer to compound uniformly with an elastomer or plastic without forming visible agglomerates, and blends thereof with elastomeric and plastic resins.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of joint application Ser. No. 140,250,now abandoned and application Ser. No. 140,249, both filed Dec. 31,1987.

BACKGROUND OF THE INVENTION

The use of polytetrafluoroethylene as an additive to enhance propertiesof elastomers or plastics has been a long-sought goal because suchblends have improved properties such as tear, flame or abrasionresistance over those of the base resin. However, because fibrils andagglomerates of polytetrafluoroethylene (PTFE) ordinarily develop whenPTFE is subjected to shear forces during compounding with other resins,the resulting blends are nonuniform and may show excessive modulus andhave warping problems. Furthermore, due to the fibrillation andagglomeration, blends which contain known polytetrafluoroethylene resinsare difficult to prepare and process especially at high additive levels.

The incorporation of fluoropolymers such as polytetrafluoroethylene andsuch polymers modified with comonomer into elastomers or thermoplasticshas been attempted before. High molecular weight, non-melt-processiblepolymers of tetrafluoroethylene, including those which contain smallamounts of comonomers such as hexafluoropropylene, tend to draw out intofibers, or fibrillate, when sheared. Although it is a useful propertyfor some applications such as paste extrusion onto wire, thisfibrillation causes problems when the polytetrafluoroethylene ormodified polytetrafluoroethylene is to be incorporated into an elastomeror a thermoplastic. The fibrillating tetrafluoroethylene polymer formsvisible agglomerates and results in undesirable increases in moduluswhen incorporated into elastomers. When compounded into thermoplastics,the fibrillating tetrafluoroethylene polymer causes undesirable meltswell when the polymer melt is forced through an orifice such as the dieat the end of an extruder. The addition of melt-processiblefluorocopolymers such as Teflon® FEP or PFA fluorocarbon resins or lowmolecular weight, irradiated PTFE, to elastomers or thermoplasticsavoids the problems of fibrillation but this approach does not improvecertain properties of the elastomer or thermoplastic.

SUMMARY OF THE INVENTION

Modified polytetrafluoroethylen (PTFE) resins produced by the dispersionprocess have now been found which can be compounded with elastomers orplastics without the agglomeration or fibrillation that occurs withknown modified polytetrafluoroethylene resins. The resins of thisinvention improve the tear strength and abrasion resistance ofelastomers, and improve the extrusion rates, abrasion resistance andflame resistance of plastics. The resins avoid the agglomeration andexcessive increases in modulus that usually occur when ordinarypolytetrafluoroethylene is added to elastomers and plastics, and theyavoid melt-swell when used with plastics.

The modified polytetrafluoroethylene resins of this invention compriserecurring units of tetrafluoroethylene (TFE) and modifying recurringunits of at least one ethylenically unsaturated comonomer that iscopolymerizable with the TFE in a dispersion process to produce anon-melt-processible tetrafluoroethylene copolymer that has enoughcomonomer units present near the surface of the copolymer particles tocause the copolymer to compound uniformly with an elastomer or plasticresin without forming visible agglomerates. Preferred comonomers includehexafluoropropylene, perfluoro(alkyl vinyl ethers), preferably whereinthe alkyl group is of 1-4 carbon atoms, or mixtures thereof. Thecomonomer is present in an amount greater than usually employed incommercial comonomer-modified polytetrafluoroethylene, but not in anamount great enough to cause the polytetrafluoroethylene to lose itsnon-melt-fabricable character. Other comonomers which are believed to beuseful include, for example, chlorotrifluoroethylene and perfluoro(alkylvinyl ethers) wherein the alkyl group is replaced with ahexafluoropropylene oxide oligomer.

It is believed that it is the presence of sufficient comonomer near theparticle surface (the shell) which inhibits the fibrillation andagglomeration that occur with previously known polytetrafluoroethyleneresins when sheared, as in blending with other polymers. While thecomonomer must be present near the surface, the comonomer may be presentthroughout the copolymer particle if desired, for example, in the coreas well as in the shell.

Generally, and usually preferably, the copolymer, that is, the modifiedpolytetrafluoroethylene, has sufficient molecular weight and enoughcomonomer in the shell so that the tensile elongation at break isgreater than 60%, the ratio of yield strength to break strength isgreater than 0.50, preferably greater than 0.60, and the rheometerpressure is less than 3500 psi (24.1 MPa), preferably between 1000 psi(6.9 MPa) and 2500 psi (17.2 MPa). The rheometer pressure of the resinis measured by adding 19.2 weight percent "Varsol" hydrocarbon lubricantand extruding the resin through a 1600/1 reduction ratio die. The highcomonomer content of the resin causes its rheometer pressure range to besubstantially lower than those of commercially availablepolyetrafluoroethylene resins, whether modified with comonomer units orunmodified. It is to be understood, therefore, that the invention hereinmay involve the use of monomers which are well known in the art, andthat such monomers may have been previously copolymerized. For example,it is known to copolymerize tetrafluoroethylene and hexafluoropropylene,and tetrafluoroethylene and a perfluoro(alkyl vinyl ether), but it isnot known to copolymerize these monomers in such a way as to produce themodified polytetrafluoroethylenes of this invention.

When blended into an elastomer or a plastic resin by a procedure thatinvolves shearing action, the modified polytetrafluoroethylene resinwill be present in the form of platelets. The platelets are roughlyoblong, having a size of between about 10-500 μm in length and aboutone-tenth that in thickness. In preferred embodiments, they are about10-100 μm in length, 5-10 μm in width and 2-5 μm in thickness. They canbe isolated, as will be discussed in greater detail hereinafter.

This invention also resides in blends which comprise

(a) an elastomeric organic resin or a plastic organic resin, and

(b) 0.1 to 200 parts per 100 parts of component (a) of adispersion-process-produced non-melt-processible tetrafluoroethylenecopolymer, said copolymer being present in said resin in the form ofplatelets distributed throughout the resin.

The resulting elastomeric blends have improved tear strength andabrasion resistance. The resulting plastic blends have improvedextrusion properties, such as, rates, abrasion resistance and flameresistance and less melt-swell.

DEFICIENCIES OF THE PRIOR ART

Polymerization to make high molecular weight non melt-processible,dispersion-process-produced PTFE resins is well known. The modificationof these resins with comonomers and the addition of chain-transfer-agentpartway through the polymerization have also been disclosed (such as inU.S. Pat. No. 3,142,665). However, the objectives of these disclosureshave clearly been to obtain a resin which fibrillates under shear andwhich is a suitable resin for "paste extrusion." This is shown by thefact that the lowest rheometer pressure which the aforesaid U.S. patentdiscloses is 4700 psig (32.4 MPa), whereas the desired rheometerpressure herein is much lower (1000-3500 psig) (6.9-24.1 MPa).

The incorporation of fluoropolymers such as polytetrafluoroethylene intoelastomers or thermoplastics has been attempted before. The resins ofthis invention avoid some of the problems of previously knownfluoropolymers and/or show advantages not previously known. Highmolecular weight, non-melt-processible polymers of tetrafluoroethylene,including those which contain small amounts of comonomers such ashexafluoropropylene, tend to draw out into fibers, or fibrillate, whensheared. Although it is a useful property for some applications such aspaste extrusion onto wire, this fibrillation causes problems when thepolytetrafluoroethylene or modified polytetrafluoroethylene is to beincorporated into an elastomer or a thermoplastic. The fibrillatingpolytetrafluoroethylene forms visible agglomerates and results inundesirable increases in modulus when incorporated into elastomers. Whencompounded into thermoplastics, the fibrillating polytetrafluoroethylenecauses undesirable melt swell when the polymer melt is forced through anorifice such as the die at the end of an extruder. The addition ofmelt-processible fluorocopolymers such as Teflon® FEP or PFAfluorocarbon resins or low molecular weight, irradiated PTFE, toelastomers or thermoplastics avoids the problems of fibrillation butthis approach does not improve certain properties of the elastomer orthermoplastic. In contrast, the resins of the present invention do notcause the above-mentioned problems but do improve certain elastomer orthermoplastic properties.

DETAILED DESCRIPTION OF THE INVENTION

The modified polytetrafluoroethylene polymers of this invention areunusual in that unlike most dispersion-produced polytetrafluoroethylenepolymers:

(1) They cannot be successfully paste extruded because their greenstrength is too low,

(2) They form platelets on shear blending into elastomeric compositionsinstead of fibrillating,

(3) Their ratio of yield strength to break strength generally is over0.50, whereas for usual dispersion-produced polymers it generally isbelow 0.5,

(4) Their extrusion pressure is less than 3500 psi (24.1 MPa), whereasfor usual dispersion-produced polymers it is over 3500 psi (24.1 MPa).

The tetrafluoroethylene copolymers of this invention are made frommonomers that are polymerized in aqueous dispersion containing adispersing agent present in amounts sufficient to cause the polymerparticles to remain in dispersed form during polymerization, and thenthe polymer dispersion is coagulated under low shear to obtain theparticles, and the particles are then separated and dried. Theseparticles are called "dispersion-process-produced" particles.

This procedure is described generally in U.S. Pat. No. 3,142,665, supra.Briefly, polymerization is carried out in a gently agitated aqueousmedium with the monomers added under pressure. The medium contains anon-telogenic dispersing agent, such as ammonium perfluorooctanoate orcaprylate. The amount of dispersing agent can range from 0.05 to 0.5% byweight of water used, and it can be added in increments if desired.

Any suitable initiator such as is described in U.S. Pat. No. 3,142,665can be used. A preferred system is a mixture of ammonium persulfate anddisuccinic acid peroxide. The initiator amount can vary widely; butgenerally will be between 0.0005 to 0.3% by weight of water. Theinitiator is added at the beginning of the reaction, and may also beadded subsequently. Chain transfer agents may also be used and added inthe same manner.

As to hexafluoropropylene (HFP), the amount present in the copolymer isat least 0.08 weight percent, and can be as high as 0.9 weight percent,although the upper limit is not critical, so long as the copolymerremains non-melt-fabricable. HFP content is determined by the methoddescribed at column 5, lines 1-12, of U.S. Pat. No. 3,142,665.

For perfluoro(alkyl vinyl ethers), especially of 1-4 alkyl carbon atoms,the amount present should be greater than 0.02 weight percent, and canbe as high as 0.3 weight percent. The perfluoro(alkyl vinyl ether)content is determined by Fourier Transform (FT) infrared (IR)spectroscopy. The C-0-C band occurs at 995 cm⁻¹ for perfluoropropylvinyl ether (PPVE) and at 985 cm⁻¹ for perfluoromethyl vinyl ether(PMVE). A 0.3 g sample of the polymer is leveled between pieces ofaluminum foil in a cylindrical mold, 2.86 cm in inside diameter. Apressure of 1409 kg/cm² is applied for one minute at ambienttemperature. The pressed sample, about 0.025 cm thick, is then analyzedby IR. The sample is scanned from 1040 to 877 cm⁻¹. A straight base lineis drawn from the absorbance minimum at 1010 cm⁻¹ to that at 889 cm⁻¹.The ratio of the absorbance from the base line to the at 985 cm⁻¹ or 995cm⁻¹, as the case may be, to the absorbance from the base line to themaximum at 935 cm⁻¹ is obtained. The actual weight percentperfluoro(propyl vinyl ether) is obtained by multiplying the ratio by0.14 (determined from a calibration curve). No calibration curve wasestablished for PMVE, but a greater proportion of that added is probablyincorporated into the polymer since it is more reactive than PPVE.

A sufficient amount of comonomer must be in the outer portion (theshell) of the copolymer particle. If the comonomer is highly reactive inpolymerization, it must be added toward the end of the polymerization toensure its presence in the outer portion (which is formed last). If thecomonomer is not highly reactive, it can be added at the beginning ornear the end; or the comonomer/TFE ratio can be increased toward the endof the reaction.

It has been found that the addition of perfluorobutyl ethylene as athird comonomer may reduce formation of coagulum in the polymerizationvessel during polymerization.

When the polymerization is complete, the polymer in the polymerizationmedium is coagulated by conventional procedures, such as described inU.S. Pat. No. 3,142,665, supra, then dried. Coagulation will occur byuse of mild agitation and/or by chemical coagulation. Alternatively, thedispersion can be treated chemically, first with a gelling agent, andthen with a water-immiscible liquid, to agglomerate the resin, with orwithout some other filler, as described in various publications, such asin U.S. Pat. Nos. 4,451,616 and 4,368,296.

The tetrafluoroethylene copolymers of this invention arenon-melt-fabricable. By this is meant that no melt flow is detected whentested by the standard melt viscosity determining procedure formelt-processible polymers. This test is according to American Societyfor Testing and Materials test D-1238-52T, modified as follows: Thecylinder, orifice and piston tip are made of a corrosion-resistantalloy, Haynes Stellite 19, made by Haynes Stellite Co. The 5.0 g sampleis charged to the 9.53 mm (0.375 inch) inside diameter cylinder, whichis maintained at 380° C. Five minutes after the sample is charged to thecylinder, it is extruded through a 2.10 mm (0.0825 inch) diameter, 8.00mm (0.315 inch) long square-edge orifice under a load (piston plusweight) of 5000 grams. This corresponds to a shear stress of 44.8 Kpa(6.5 pounds per square inch). If any melt extrudate is observed, it isso noted.

The resins of this invention have an unusually low rheometer pressure, ahigh level of elonation and a high ratio of yield strength to breakstrength. They are non-agglomerating and non-fibrillatible, which may bedue to the presence of the higher comonomer concentration in the shellthan heretofore was present in known modified polytetrafluoroethylenepolymers.

The tetrafluoroethylene copolymers of this invention have low breakstrengths, but about the same yield strength as commercially availableresins (thus higher ratios of yield to break strengths). This indicatesthat the resin's apparent modulus (stiffness) due to drawing is less forthese copolymers. They also have low rheometer pressures. Both of theseobservations indicate less fibril or other molecular orientation uponstressing the polymer. This may explain, in part, why uniform blends ofthese resins in elastomers and other polymers are easier to prepare andhave lower moduli than those obtained with known non-melt-processibleresins. Reduced fibrillation will allow more uniform blends but sometoughness as indicated by a minimum elongation is also required for thefluoropolymer to reinforce the other plastics or elastomers. Theelongation of a modified PTFE resin is a function of its molecularweight and of the resin comonomer content and type. A reduced PTFEhomopolymer molecular weight will reduce the tendency to form fibrilsduring shear but if the molecular weight is reduced enough toessentially stop fibril formation, the elongation of the resulting resinis too low for it to reinforce another elastomer or plastic. It has beenfound that the presence of some minimum level of comonomer other thanTFE will drastically reduce the tendency to fibrillate without asignificant drop in molecular weight and thus elongation. The comonomermay also alter the resin crystallinity and change the form of the drawnfluoropolymer resin from fibril to elongated sheets or plates. Thecombination of properties achieved by means of the invention herein hasheretofore never been available in the art.

As stated hereinabove, the blends of the invention are blends of anelastomer or plastic with 0.1 to 200 parts per 100 parts of elastomer orplastic, of the aforesaid dispersion-produced non-melt-processibletetrafluoroethylene copolymer. Preferably, larger amounts of thecopolymer are usually used for elastomers, for example, 1 to 200 partsper 100 parts of elastomer. For plastics, the amount is preferably0.1-40 parts per 100 parts of plastic.

No separate phases are visible to the naked eye in compounded blends ofthe new resins in other plastics or elastomers. Photomicrographs ofblends show that even at a magnification as high as 2000X using anoptical microscope, no fibrous structure is apparent. If the refractiveindices of the blended materials are different, a platelet structure isseen in which the platelet size preferabley ranges from 10-100 μm long,5-10 μm wide, and 2-5 μm thick. At high concentrations in the matrix,the plate-like particles may be interconnected to form discontinuoussheets. The platelets of this invention can be isolated by shearing theresin of this invention in a solid water-soluble salt, and thendissolving the salt in water, leaving the platelets.

The term "elastomer" as used herein has its normal meaning in the art,that is, the cross-linked material, after being stretched to twice itsnormal length and released will return with force to substantially itsoriginal length. The term "plastic" as used herein has its usual meaningin the art, that is, it is a normally rigid, high molecular weightthermoplastic or thermosetting organic polymer, usually possessing somecrystallinity or glass-like behavior.

The elastomer matrix of the blend can be any elastomer including, butnot limited to, vinylidene fluoride copolymers, for example, vinylidenefluoride/hexafluoropropylene (VF2/HFP) copolymers; VF2/HFP/TFEcopolymers; TFE/PMVE copolymers; ethylene/propylene/diene (EPDM)copolymers; styrene/butadiene copolymers; polychloroprene;chlorosulfonated polyethylene; silicones; fluorosilicone elastomers; andnatural rubber. The elastomer can be uncured or it can contain curingingredients and be cured. The uncured elastomer has a Mooney Viscosity,ML-4 (100° C.) greater than 1. The plastic matrix can be any plasticincluding, but not limited to, polyolefins, for example, polyethylene(PE); polypropylene (PP); polyamides, for example, nylon; polysulfones(PS); polyvinylidene fluoride (PVDF); epoxies; polyether ether ketones(PEEK); and melt processible copolymers of tetrafluoroethylene, such astetrafluoroethylene/hexafluoropropylene (TFE/HFP); andtetrafluoroethylene/perfluoro(propyl vinyl ether) (TFE/PPVE) copolymers.

The elastomeric or plastic matrix can contain fillers, such asreinforcing agents or fire retarding agents. The plastic matrix may becharacterized as thermoplastic or thermosetting. The modifiedpolytetrafluoroethylene resins of this invention can be mixed into theelastomer or plastic using conventional techniques and equipment, suchas a two-roll mill, a Banbury Internal Mixer, or a twin-screw orsingle-screw extruder. The shear strain rate during mixing is typicallygreater than 10 sec-1 , for example, between 10 and 1000 sec-1.Different levels of comonomer content can be used, depending on thelevel of shear during subsequent compounding. The more comonomer presentin the PTFE resin, the less sensitive the resin is to compounding shearlevels. The combination of the degree of resin comonomer modification,the loading level in the elastomer or plastic, and the shear level ofblending is such that no fibrils develop.

ANALYTICAL TESTS FOR THE TFE COPOLYMER RESINS

Samples of the tetrafluoroethylene copolymers were molded and sinteredas described in ASTM D-1457 for the measurement of tensile properties.Microtensile bars were cut and tested as described in ASTM D-1708-80 ata strain rate of two inches per minute (5.1 cm/min).

Rheometer pressure was measured in accordance with ASTM D-1457-83Section 12.8, except that the resin was not sieved before mixing withthe "Varsol" lubricant and the preform was made in a 26 mm diameterextension tube at 300 psi (2.1 MPa). Measurements were made at the 19.2%lubricant level called for in the ASTM method. For additional datapresented in the examples, some samples were tested at 18% lubricantlevel.

Standard specific gravity (SSG) was determined by water displacement ofa standard molded test specimen in accordance with ASTM D 1457-69. Thestandard molded part was formed by preforming 12.0 g of the powder(copolymer) in a 2.86 cm diameter die at a pressure of 34.5 MPa,followed by sintering the preform by heating from 300° C. to 380° C. at2° C./minute, holding at 380° C. for 30 minutes, cooling to 295° C. at1° C/minute and holding at this temperature for 25 minutes, after whichthe specimen is cooled to 23° C. and tested for specific gravity.

Raw dispersion particle size or RDPS values were determined by PhotonCorrelation Spectroscopy using a Brookhaven 2030 Correlator manufacturedby Brookhaven Instruments, Inc. of Holtsville, New York, using an argonion laser at 512.5 nm at a 90° angle, and 25° C.

The PFBE content (when this comonomer was used) of the polymer could notbe determined accurately and reproducibly by Fourier Transform infraredspectroscopy (FTIR). It was estimated to be present in the polymer equalto the amount added because of its high reactivity.

EXAMPLES 1-7

A horizontally-disposed, water-steam jacketed, cylindical stainlesssteel autoclave (clave), having a paddlewheel agitator running thelength of the autoclave, and having a length-to-diameter ratio of about1.5 to 1 and a water capacity of 39,000 parts, was charged with 20,400parts of demineralized water, 5 parts of ammonium perfluorocaprylatedispersing agent and 600 parts of paraffin wax. The autoclave contentswere heated to 70° C. and the autoclave was then evacuated and purgedwith TFE monomer. A reduced pressure was then left on the autoclave, theagitator was turned on at 43 rpm (revolutions per minute) and thecontents were heated up to 88° C. Perfluorobutylethylene (PFBE) and/orhexafluoropropylene (HFP) were added to the autoclave and sufficienttetrafluoroethylene (TFE) was added to achieve an autoclave pressure of380psig (2.6 MPa). Then 500 parts of the first initiator solution waspumped into the autoclave. After kickoff occured (10 psig or 0.07 MPadrop in pressure), the temperature of the reaction mixture wascontrolled at 90° C. for the duration of the polymerization. Theagitator speed was maintained at 43 rpm and the autoclave pressure wasmaintained at 380 psig (2.6 MPa) by the addition of tetrafluoroethylenemonomer until the desired level of tetrafluoroethylene addition wascomplete. When 1360 parts of tetrafluoroethylene had been added afterkickoff, 1000 parts of a solution of 25 parts ammoniumperfluorocaprylate in demineralized water was pumped to the autoclave at50 parts/minute. After 6800 parts of tetrafluoroethylene had been addedafter kickoff, 300 parts of a second initiator/methanol solution indemineralized water was added to some of the batches. After thespecified tetrafluoroethylene addition was complete (measured afterkickoff), the reaction was continued until the pressure reacted down to185 psig (1.3 MPa). The autoclave was then vented to atmosphericpressure and the dispersion was dropped from the autoclave. Aftercooling, the supernatant paraffin wax was removed and weighed. Thedispersions were coagulated by stirring or by the chemicalgelation/solvent agglomeration method to give a powder which wasseparated and then dried at 150° C. for four days. A summary of theexamples and product analyses is given in Tables I and II.

EXAMPLE 8

The autoclave described in Examples 1-7 was charged with 20,400 parts ofdemineralized water, five parts of ammonium perfluorocaprylatedispersing agent and 600 parts of paraffin wax. The autoclave contentswere heated to 80° C. and the autoclave was then evacuated and purgedwith TFE monomer. A reduced pressure was then left on the autoclave andit was heated up to 88° C. after which it was pressured up to 380 psig(2.6 MPa) with tetrafluoroethylene monomer. The agitator was turned onat 43 rpm and 500 parts were added to the autoclave of a solution of 1.2parts ammonium persulfate, 15 parts disuccinic acid peroxide, and 3parts methanol made up to 1500 parts with demineralized water. Afterkickoff occurred (10 psig or 0.07 MPa drop in pressure), the temperatureof the reaction mixture was controlled at 90° C. for the duration of thepolymerization. The agitator speed was maintained at 42 rpm and theautoclave pressure was maintained at 380 psig (2.6 MPa) by the additionof tetrafluoroethylene monomer. When 1360 parts of tetrafluoroethylenehad been added after kickoff, 1000 parts of a solution of 25 parts ofammonium perfluorocaprylate in demineralized water was pumped into theautoclave at 50 parts/minute. When 5900 parts of tetrafluoroethylenemonomer had been added after kickoff, the monomer feed was stopped andthe pressure was allowed to react down to 185 psig (1.3 MPa). Theautoclave was then vented to 15-20 psig (0.11-0.14 MPa) with theagitator turned off. About 78 parts of hexafluoropropylene were pumpedinto the clave and the autoclave was then repressurized to 380 psig (2.6MPa) with tetrafluoroethylene. Another 300 parts of theinitiator/methanol solution described above were pumped into theautoclave simultaneously with tetrafluoroethylene repressurization. Theagitator was turned on and the speed raised slowly to 40 rpm where itwas held for the remainder of the polymerization. After kickoff againoccurred, tetrafluoroethylene monomer was added to maintain the 380 psig(2.6 MPa) pressure. After 3630 parts of tetrafluoroethylene had beenadded after the second kickoff, the agitator was turned off and theautoclave was vented to atmospheric pressure. The dispersion was thendropped from the autoclave at atmospheric pressure and cooled. Thedispersion was coagulated by stirring to give a powder which was thenisolated and dried at 150° C. for four days. The polymer contained 0.16weight percent hexafluoropropylene and had an SSG of 2.271. The ratio ofpolymer weight polymerized during the two stages of reaction was 65/35including the reaction of a portion of the tetrafluoroethylene used topressurize the autoclave. The calculated hexafluoropropylene content ofthe polymer made during the second reaction stage was 0.45 weightpercent.

The example was repeated five times and the polymer of all 6 runs wasblended.

The product data for the blend are shown in Table III.

EXAMPLE 9

The autoclave described in the previous examples was charged with 20900parts of demineralized water and 15 parts of ammonium perfluorocaprylatedispersing agent. The autoclave contents were heated to 65° C. and theautoclave was then evacuated and purged with TFE monomer. A reducedpressure was left on the autoclave, the agitator was then turned on at43 rpm and 14.5 parts of perfluorobutyl ethylene and 78 parts ofhexafluoropropylene were added. The autoclave was heated to 88° C. andit was then pressured up to 380 psig (2.6 MPa) with TFE monomer. Then500 parts were added to the autoclave of a solution of 14 partsdisuccinic acid peroxid (DSP) and 0.4 parts ammonium persulfate (APS)made up to 1000 parts with demineralized water.

After kickoff occurred (10 psig or 0.07 MPa drop in pressure), thetemperature of the reaction mixture was controlled at 90° C. for theduration of polymerization. The agitator speed was maintained at 43 rpmand the autoclave pressure was maintained at 380 psig (2.6 MPa) by theaddition of TFE monomer until 8170 parts of TFE had been added afterkickoff. When 1360 parts of TFE had been added after kickoff, 1000 partsof a solution of 25 parts ammonium perfluorocaprylate in demineralizedwater was pumped into the autoclave at 90 parts/minute. After 5450 partsof TFE had been added after kickoff, 300 parts of a solution of 10.0parts disuccinic acid peroxide, 1.0 parts ammonium persulfate, and 5.0parts methanol made up to 1000 parts with demineralized water was addedto the autoclave at 50 parts/minute. The TFE feed was cut off after theaddition of 8170 parts TFE (measured after kickoff). Agitation wascontinued until the autoclave pressure reacted down to 185 psig (1.3MPa). The autoclave was vented to atmospheric pressure and thedispersion was dropped from the autoclave. The dispersion, whichcontained about 30.5% solids, was coagulated by stirring to give apowder which was dried in a 150° C. oven for four days. Product data areshown in Table III.

EXAMPLE 10

The autoclave described in the previous examples was charged with 20,800parts of demineralized water, 5 parts of ammonium perfluorocaprylate,and 600 parts of paraffin wax. With the autoclave contents at 65° C.,the autoclave was evacuated and purged with tetrafluoroethylene. Areduced pressure was left on the autoclave and it was heated to 85° C.with the agitator on at 43 rpm. The autoclave was then pressured to 380psig (2.6MPa) with tetrafluoroethylene monomer and 500 parts were addedto the autoclave of a solution of 1.0 part APS, 10 parts DSP, and 5parts methanol made up to 1000 parts with demineralized water. Afterkickoff (10 psig or 0.07 MPa drop in pressure) occurred, the temperatureof the reaction mixture was maintained at 85° C. for the duration of thepolymerization. The agitator speed was held at 43 rpm and the autoclavepressure was maintained at 380 psig (2.6 MPa) by the addition oftetrafluoroethylene monomer. When 1360 parts of tetrafluoroethylene hadbeen added after kickoff, 1000 parts of a solution of 25 parts ammoniumperfluorocaprylate in demineralized water was pumped into the autoclaveat 50 parts/minute. When 5900 parts of tetrafluoroethylene had beenadded to the autoclave after kickoff, monomer feed and the agitator werestopped and the autoclave contents were cooled to below 75° C. Theautoclave was vented and then evacuated to 5" of mercury vacuum. A valveto a cylinder of perfluoromethylvinyl ether (PMVE) was then openedallowing 7.8 parts of the PMVE to enter the autoclave. The valve wasthen closed, the agitator was restarted at 43 rpm, and the autoclavecontents were heated to 85° C. The autoclave was then againrepressurized to 380 psig (2.6 MPa) with tetrafluoroethylene monomer and270 parts were added to the autoclave of a solution of 1.0 part APS, 10parts DSP, and 5 parts methanol made up to 1000 parts with demineralizedwater. After kickoff (10 psig or 0.07 MPa drop in pressure) occurred,the temperature of the reaction mixture was maintained at 85° C. for theduration of the polymerization. The agitator speed was held at 43 rpmand the autoclave pressure was maintained at 380 psig (2.6 MPa) by theaddition of tetrafluoroethylene monomer. After 1360 parts oftetrafluoroethylene had been added after the second kickoff, the monomerfeed was cut off and the pressure was allowed to react down to 185psig(1.3 MPa). The agitator was then turned off and the autoclave wasvented. The dispersion was dropped from the autoclave and cooled. Thedispersion was coagulated by stirring and the polymer powder was driedat 150° C. for 3 days.

Product data are included in the Table III.

EXAMPLE 11

This polymerization and product isolation was carried out in a similarmanner to Example 10 with two exceptions: 1) 14.5 parts ofperfluorobutylethylene (PFBE) were added to the autoclave after purgingand evacuating (before tetrafluoroethylene addition) and 2) the amountof PMVE added was 7.7 parts.

The product data are included in Table III.

EXAMPLE 12

The clave described in the previous examples was charged with 20,900parts of demineralized water, 600 parts of paraffin wax, and 1.3 partsof ammonium perfluorocapyrlate dispersing agent. The clave content wereheated to 65° C. and the clave was then evacuated and purged with TFEmonomer. A reduced pressure was left on the clave and 7.7 parts ofperfluoropropylvinyl ether (PPVE) were added. The agitator was turned onat 46 rpm and the clave was heated to 75° C. The clave was thenpressured up to 400 psig with TFE monomer. Then 250 parts were added tothe clave at the rate of 50 parts/minute of a solution of 1.4 partsammonium persulfate made up to 1000 parts with demineralized water.After kickoff occurred (10 psig or 0.07 MPa drop in pressure), thetemperature of the reaction mixture was controlled at 75° C. for theduration of polymerization. The agitator speed was maintained at 46 rpmand the clave pressure was maintained at 400 psig (2.6 MPa) by theaddition of TFE monomer. When 1360 parts of TFE had been added afterkickoff, 1000 parts of a solution of 29 parts ammoniumperfluorocaprylate in demineralized water was pumped into the clave at90 parts/minute. After 7490 parts of TFE had been added after kickoff,1000 parts of a solution of 10.0 parts succinic acid, 0.7 part ammoniumpersulfate, and 0.7 part methanol made up to 1000 parts withdemineralized water was added to the clave at 50 parts/minute.Simultaneously the reactor pressure setpoint was reduced to 200 psig andthe pressure was reacted down to that level. This procedure increasedthe PPVE/TFE monomer ratio. The TFE feed was then continued until 11,800parts of TFE (measured after kickoff) had been added to the reactor. Theagitator was then turned off, the clave was vented to atmosphericpressure, and the dispersion was dropped from the clave. The dispersion,which contained about 37.8% solids, was coagulated by stirring to give apowder which was separated and then dried in a 150° C. oven for threedays.

Product data are shown in Table III.

EXAMPLE 13

In this example, polymerization was carried out as in Example 13 withthe following exceptions: (1) the reactor precharge contained 1.0 partammonium perfluorocaprylate, 5 parts succinic acid, 20,900 partsdemineralized water, and 600 parts of paraffin wax,(2) the amount ofPPVE added after evacuation was 12.2 parts and (3) the second initiatorsolution, added after 7490 parts of TFE addition, contained 0.7 part ofammonium persulfate and 0.7 part of methanol (no succinic acid) made upto 1000 parts with demineralized water. The resin was coagulated anddried.

Product data are shown in Table III.

EXAMPLE 14

A blend of 1 part of polymer powder from Example 8 with 19 partsgranular potassium chloride was placed in a oven at 100° C. for twohours. The blend was then removed from the oven and immediately pouredinto a preheated (100° C.) mortar where it was ground with a pestle forone minute. The potassium chloride was then dissolved away with awater/methanol mixture, leaving the polymer. After drying at 150° C.,the polymer was examined with a microscope and was found to be presentprimarily as platelets from 10 to 500 micrometers across and about onetenth as thick.

As a control, 5 parts of a commercial "fine powder" paste extrusionresin, which contained HFP as a modifier, was treated identically tothat above. The polymer, after washing and drying, was present asfibrous agglomerates. There was no evidence of the platelet structure.

                                      TABLE I                                     __________________________________________________________________________    POLYMERIZATION SUMMARY EXAMPLES 1-7                                           __________________________________________________________________________                 First Initiator                                                                           Second Initiator/                                                 Methanol Solution                                                                         Methanol Solution                                        Wax                                                                              HFP                                                                              PFBE                                                                             APS.sup.1                                                                         DSP.sup.2                                                                         Methanol                                                                          APS  DSP                                                                              Methanol                                     Ex. No.                                                                           parts                                                                            parts                                                                            parts                                                                            parts                                                                             parts                                                                             parts                                                                             parts                                                                              parts                                                                            parts                                        __________________________________________________________________________    1   600                                                                              78 14.5                                                                             0.9 7.5 1.0 0.54 4.5                                                                              0.6                                          2   600                                                                              78 0  0.73                                                                              6.0 0.8 0.44 3.6                                                                              0.5                                          3   600                                                                              78 14.5                                                                             0.83                                                                              6.9 1.4 0.50 4.2                                                                              0.8                                          4   600                                                                              78 14.5                                                                             0.90                                                                              7.5 1.0 0    0  0                                            5   600                                                                              78 14.5                                                                             0.83                                                                              6.9 1.4 0    0  0                                            6   600                                                                              86 14.5                                                                             0.25                                                                              7.0 0.5 0.39 3.0                                                                              1.2                                          7   600                                                                              78 0  0   7.0 1.0 0.30 4.2                                                                              0.9                                          __________________________________________________________________________                       TFE                                                                           Added After                                                                   Kickoff                                                                              Dispersion RDPS                                                    Ex. No.                                                                           parts  % Solids                                                                           micrometers                                    __________________________________________________________________________                   1   9900   36.5 0.196                                                         2   9900   36.5 0.220                                                         3   9900   35.2 0.191                                                         4   9900   35.3 NM                                                            5   6800   28.3 0.174                                                         6   9900   35.8 NM                                                            7   9900   34.7 0.232                                          __________________________________________________________________________     .sup.1 APS means ammonium persulfate                                          .sup.2 DSP means disuccinic acid peroxide                                     NM means not measured.                                                   

                                      TABLE II                                    __________________________________________________________________________    PRODUCT SUMMARY, EXAMPLES 1-7                                                            1600/1                                                                        Rheometer Pressure                                                                      Tensile       Melt                                                  18.0%                                                                              19.2%                                                                              Yield/Break                                                                          Tensile                                                                              Flow                                               %  "Varsol"                                                                           "Varsol"                                                                           Strength                                                                             Elongation                                                                           at                                         Ex. No.                                                                            SSG                                                                              HFP                                                                              (MPa)                                                                              (MPa)                                                                              Ratio  at Break, %                                                                          380° C.                             __________________________________________________________________________    1    2.225                                                                            0.52                                                                             17.0 10.5 1.00   355    No                                         2    2.253                                                                            0.41                                                                             18.0 11.0 1.26   155    No                                         3    2.227                                                                            0.29                                                                             20.9 11.5 0.76   445    No                                         4    2.228                                                                            0.40                                                                             24.8 NM   1.18   193    NM                                         5    2.209                                                                            0.29                                                                             24.7 12.0 0.80   368    No                                         6    2.213                                                                            0.29                                                                             23.6 NM   0.68   439    No                                         7    2.247                                                                            0.30                                                                             20.6 NM   0.94   408    No                                         __________________________________________________________________________     NM means not measured.                                                   

                                      TABLE III                                   __________________________________________________________________________    PROPERTY DATA SUMMARY FOR EXAMPLES 8-13                                                          1600/1 Rheometer                                                              Pressure                                                                      18.0%                                                                              19.2%                                                                              Tensile                                                    Comonomer                                                                              "Varsol"                                                                           "Varsol"                                                                           Yield/Break                                                                          Elongation                                                                          Melt Flow at                        Example No.                                                                          SSG                                                                              Type                                                                              Level                                                                              (MPa)                                                                              (MPa)                                                                              Ratio  at Break                                                                            380° C.                      __________________________________________________________________________    8      NM HFP 0.16%                                                                              16.4 8.5  1.29   447%  No                                  (Blend of                                                                     six runs)                                                                     9      2.198                                                                            HFP 0.29%                                                                              20   11.4 0.58   427   No                                  10     2.274                                                                            PMVE                                                                              0.090%*                                                                            12.0 NM   1.21   416   NM                                  11     2.219                                                                            PMVE                                                                              0.089%*                                                                            22.1 11.0 0.57   522   No                                  12     2.179                                                                            PPVE                                                                              0.03%                                                                              25.6 21.6 0.53   400   No                                  13     2.179                                                                            PPVE                                                                              0.04%                                                                              28.9 23.1 0.54   474   NM                                  __________________________________________________________________________     *Comonomer levels shown are levels added to batch.                            NM means not measured.                                                   

The following examples describe blending of the modifiedpolytetrafluoroethylene resins with elastomers and thermoplastics.

EXAMPLE 15

A modified PTFE fine powder copolymer resin was prepared as in Example8. Samples of the modified PTFE copolymer were mixed with a 45 MooneyViscosity elastomeric VF2/HFP 60:40 (by weight) copolymer (vinylidenefluoride/hexafluoropropylene), fillers and curatives on a two rollrubber mill at a shear strain rate of about 100 sec⁻¹ for 10 minutesaccording to the following recipe.

    ______________________________________                                                     A(Control)                                                                            B       C       D                                        Sample         Parts                                                          ______________________________________                                        VF2/HFP copolymer                                                                            96        96      96    96                                     Example 8 PTFE polymer                                                                       --        10      20    30                                     Carbon Black (MT Black)                                                                      30        30      30    30                                     Ca(OH).sub.2   6         6       6     6                                      MgO            3         3       3     3                                      Additive 1*    1.28      1.28    1.28  1.28                                   Additive 2**   2.8       2.8     2.8   2.8                                    ______________________________________                                         *A 2:1 blend of a VF2/HFP copolymer with benzyltriphenylphosphonium           chloride.                                                                     **A 48:50:2 blend of a VF2/HFP copolymer with bisphenol AF and rice bran      wax.                                                                     

After mixing, sheets were formed and press-cured at 177° C. for 15minutes, then post cured at 232° C. for 24 hours.

Samples were die cut from the cured sheet and tested at 25° C. and 177°C. for tear strength according to ASTM method D 470 and for tensileproperties according to ASTM method D 412. Measurements were made bothin the direction of mill rotation and transverse direction and thenaveraged.

    ______________________________________                                        Sample         A(Control)                                                                              B       C     D                                      ______________________________________                                        Tested at 25° C.                                                       Tear Strength (kN/m)                                                                         4         6       7     7                                      M.sub.100 (MPa)                                                                              4         5       7     9                                      TB (MPa)       15        15      15    16                                     EB (%)         260       260     250   230                                    Tested at 177° C.                                                      Tear Strength (kN/m)                                                                         0.5       0.9     1.6   2.3                                    M.sub.100 (MPa)                                                                              --        4       4     4                                      TB (MPa)       3         4       5     6                                      EB (%)         95        225     125   110                                    ______________________________________                                         M.sub.100 = Modulus at 100% elongation.                                       TB = Tensile strength.                                                        EB = Elongation at break.                                                     kN/m = kiloNewtons/meter                                                 

The control blend (A) is a representative commercial VF2/HFP elastomericcopolymer formulation. All blends processed well providing smooth,rubbery homogeneous appearing slabs and test pieces. When the Example 8PTFE polymer was mill-mixed into the VF2/HFP copolymer, duringpreparation of samples B, C and D there was no agglomeration of theExample 8 PTFE polymer. Examination of test pieces, prior to addition ofblack and curatives, using an optical microscope, as well astransmission and scanning electron microscopes showed the Example 9 PTFEpolymer to be uniformly dispersed as distinct particles with no evidenceof fibrillation. Plate-like aggregates of size 10×5×2 μm, composed ofdistinct particles were observed. Comparison of samples B, C and D withthe control, A, shows that Example 8 PTFE polymer provides a significantdegree of reinforcement and improvement in tear strength at 25° C. andat 177° C., with no fibrillation or agglomeration into visible clumps ornodes.

The copolymers of Examples 4, 10 and 12 behaved in a like fashion whenblended with the VF2/HFP elastomer.

COMPARATIVE EXPERIMENT 1

This experiment shows that comonomer must be present in the TFE polymer.

A sample of 20 parts of a commercially available PTFE paste extrusionresin, which has no comonomer in the shell and which has a ratio ofyield strength to break strength of only 0.43, and which has a rheometerpressure of 35 MPa at a reduction ratio of 1600:1 was mixed with 100parts of a 45 Mooney Viscosity VF2/HFP 60:40 (by weight) elastomericcopolymer on a two roll rubber mill at a shear strain rate of about 100sec⁻¹ for 10 minutes. It was observed that the PTFE resin partiallyagglomerated into visible white clumps or nodes approximately 2-4 mm indiameter with long fine fibrils connecting the nodes. Additional mixingtended to cause further agglomeration rather than to improve dispersion.The blend had a high modulus.

COMPARATIVE EXPERIMENT 2

This experiment demonstrates that the PTFE must be non-melt-fabricable.

Two melt-fabricable copolymers based on TFE were mixed with a 45 MooneyViscosity VF2/HFP 60:40 copolymer, fillers and curatives on a two rollrubber mill at a shear strain rate of 100 sec⁻¹ for 10 minutes accordingto the following recipe:

    ______________________________________                                                     A(Control) B      C                                              Sample         Parts                                                          ______________________________________                                        VF2/HFP Copolymer                                                                            96           96     96                                         TFE Copolymer #1                                                                             --           20     --                                         TFE Copolymer #2                                                                             --           --     20                                         MT Black       30           30     30                                         Ca(OH).sub.2   6            6      6                                          MgO            3            3      3                                          Additive 1*    1.28         1.28   1.28                                       Additive 2**   2.8          2.8    2.8                                        ______________________________________                                         *A 2:1 blend of a VF2/HFP copolymer with benzyltriphenylphosphonium           chloride.                                                                     **A 48:50:2 blend of a VF2/HFP copolymer with Bisphenol AF and rice bran      wax.                                                                     

TFE copolymer #1 is a melt-fabricable, thermoplastic copolymercontaining 84 weight percent TFE and 16 weight percent hexafluoropylene;melt flow number 6.5 (ASTM D 2116). TFE Copolymer #2 is amelt-fabricable, thermoplastic copolymer containing 97 weight percentTFE and 3 weight percent perfluoropropyl vinyl ether; melt flow number13.

After mixing, sheets were formed and press-cured at 177° C. for 15minutes, then post cured at 232° C. for 24 hours.

Samples were die cut from the cured sheet and tested as in Example 15.

    ______________________________________                                        Sample          A          B      C                                           ______________________________________                                        Tested at 25° C.                                                       Tear Strength (kN/m)                                                                          4          3      3                                           M.sub.100 (MPa) 4          4      4                                           T.sub.B (MPa)   15         10     12                                          E.sub.B (%)     260        200    200                                         ______________________________________                                    

The control sample, A, is a representative commercial VF2/HFP copolymerformulation. Samples B and C, which contain melt-fabricable copolymersbased on TFE, processed well and provided smooth, rubbery, homogeneousappearing slabs and test pieces. There was no apparent agglomeration orfibrillation of the TFE based copolymer.

Comparison of samples B and C with the control, A, shows thatmelt-fabricable copolymers based on TFE do not provide any degree ofreinforcement to the elastomer and in fact reduce certain tensile andtear properties. Therefore, even though melt-fabricable copolymers basedon TFE can be added to elastomers, at high levels, with no agglomerationor fibrillation, they act as nonreinforcing fillers and have limitedvalue.

EXAMPLE 16

Dry blends were prepared of a commercially available melt-processibletetrafluoroethylene/hexafluoropropylene (TFE/HFP) copolymer, containing88% TFE and 12% HFP and having a melt flow number of 6.8, with severallevels of both a commercially available high molecular weightdispersion-process-produced TFE homopolymer powder and powder fromExample 1 above. These blends were then extruded through a combinationof a 28 mm twin-screw extruder feeding a 1.5 inch (3.81 cm) single-screwextruder which fed a die. After extrusion, the blends were passedthrough a melt indexer at 372° C. under the conditions described hereinfor measuring standard melt viscosities. The percent melt swell valueswere then obtained by comparing the diameters of the extrudates with themelt indexer orifice. The results below show that the modified resin ofExample 1 affords much less melt swell than the commercially availablePTFE homopolymer.

    ______________________________________                                        Additive to Melt-Processible TFE/HFP                                                                 Melt Swell                                             ______________________________________                                        None                   7.0%                                                   0.6% High Molecular Weight PTFE                                                                      70%                                                    3.0% High Molecular Weight PTFE                                                                      158%                                                   0.5% Example 1 Powder  7.0%                                                   1.5% Example 1 Powder  29%                                                    4.8% Example 1 Powder  30%                                                    9.1 Example 1 Powder   38%                                                    ______________________________________                                    

EXAMPLE 17

Dry blends were prepared and extruded as above of mixtures of amelt-processible tetrafluoroethylene/perfluoro(propyl vinyl ether)(TFE/FPVE) copolymer, containing 97% TFE and 3% PPVE and having a meltflow number of 13, with 3% of power from Example 1 and with 3% lowmolecular weight irradiated PTFE. Films 7-8 mils (0.1778-0.2032 mm)thick of each blend and of the unmodified copolymer were compressionmolded at 350° C. and then immediately quenched in cold water. Thefatigue resistance of the films were measured by the MIT flex life testdescribed in U.S. Pat. No. 2,946,763. It can be seen from the resultsbelow that the addition of irradiated PTFE reduced the number of flexcycles, whereas the Example 1 powder actually raised the number ofcycles to failure.

    ______________________________________                                                          Number of Flex Cycles                                       Sample            to Failure                                                  ______________________________________                                        Control of TFE/PPVE                                                           melt-processible Copolymer                                                                      4945                                                        Control resin containing                                                      3% irradiated PTFE powder                                                                       3395                                                        Control resin containing                                                      3% Example 1 powder                                                                             5535                                                        ______________________________________                                    

EXAMPLE 18 Addition of TFE Copolymer to Silicone Elastomer

The TFE copolymer of Example 8 was mixed into a commercially available,18 Mooney Viscosity fluorosilicone elastomer ("Silastic" 2311 DowCorning) along with curatives, on a two-roll rubber mill at a shear rateof about 100 sec⁻¹ for ten minutes according to the following recipe.

    ______________________________________                                                             A      B                                                 Sample               parts  parts                                             ______________________________________                                        Silicone Rubber      100    100                                               TFE Copolymer Ex. 8  --     10                                                Dicumyl Peroxide     5      5                                                 ______________________________________                                    

After mixing, sheets were formed and press-cured at 150° C. for 10minutes.

Samples were die cut (cutout with a die form) and tested as in Example15.

    ______________________________________                                        Sample                A     B                                                 ______________________________________                                        Tested at 25° C.                                                       Tear Strength (kN/m)  0.8   7                                                 M.sub.100 (MPa)       --    --                                                T.sub.B (MPa)         7     8                                                 E.sub.B (%)           80    60                                                ______________________________________                                    

The control sample, A, is a representative commercial silicone elastomerformulation. Both samples processed well, providing smooth, rubberyhomogeneous appearing slabs and test pieces. When the TFE copolymerresin was mill mixed into the silicone elastomer, during preparation ofsample B, there was no visible agglomeration of the TFE copolymer intoclumps or nodes. The copolymer was dispersed as distinct particles, withno apparent fibrillation. Comparison of sample B with the control, A,shows that TFE resin provides a significant degree of reinforcement andimprovement in tear strength.

EXAMPLE 19 Addition of TFE Copolymer to EPDM Elastomer

The TFE copolymer of Example 8 was mixed into a commercially available,40 Mooney Viscosity EFDM elastomer (Nordel® 1040; E. I. du Pont deNemours and Company) along with filler and curatives, on a two-rollrubber mill at a shear rate of about 100 sec⁻¹ for ten minutes accordingto the following recipe:

    ______________________________________                                                            A(Control)                                                                              B                                               Sample              Parts     Parts                                           ______________________________________                                        EPDM Elastomer      100       100                                             TFE Copolymer Ex. 8 --        30                                              Zinc Oxide          5         5                                               Stearic Acid        1         1                                               HAF Black           80        80                                              Paraffinic Oil      50        50                                              Zinc Dibutyldithiocarbamate                                                                       2         2                                               Tetraethyl Thiuram Disulfide                                                                      1         1                                               Zinc Mercaptobenzothiazole                                                                        1         1                                               Sulfur              1.5       1.5                                             ______________________________________                                    

After mixing, sheets were formed and press-cured at 160° C. for 20minutes.

Samples were die cut and tested as in Example 15.

    ______________________________________                                        Sample               A      B                                                 ______________________________________                                        Tested at 25° C.                                                       Tear Strength (kN/m) 6      8                                                 M.sub.100 (MPa)      1      1                                                 T.sub.B (MPa)        18     17                                                E.sub.B (%)          641    656                                               ______________________________________                                    

The control sample, A, is a representative commercial EPDM elastomerformulation. Both samples processed well providing smooth, rubberyhomogeneous-appearing slabs and test pieces. When the TFE copolymer wasmill mixed into the EPDM elastomer, during preparation of sample B,there was no visible agglomeration of the TFE resin into clumps ornodes. The resin was dispersed as distinct particles and as plate-likeaggregates of distinct particles, with no apparent fibrillation.Comparison of sample B with the control, A, shows that the PTFE resinprovides a significant improvement in tear strength to the EPDMelastomer.

EXAMPLE 20 Addition of Modified PTFE to Poltchloroprene Elastomer

The TFE copolymer resin of Example 8 was mixed into a commerciallyavailable 60 Mooney Viscosity polychloroprene elastomer (Neoprene GNA,Du Pont) along with filler and curatives, on a two-roll rubber mill at ashear rate of about 100 sec⁻¹ for ten minutes according to the followingrecipe:

    ______________________________________                                                           Parts                                                      Sample               A      B                                                 ______________________________________                                        Polychloroprene      100    100                                               TFE Copolymer Ex. 8  --     30                                                Stearic Acid         0.5    0.5                                               SRF Black            30     30                                                Zinc Oxide           5      5                                                 Magnesium Oxide      4      4                                                 ______________________________________                                    

After mixing, sheets were formed and press-cured at 153° C. for 30minutes.

Samples were die cut and tested as in Example 15.

    ______________________________________                                        Sample               A      B                                                 ______________________________________                                        Tested at 25° C.                                                       Tear Strength (kN/m) 6      11                                                M.sub.100 (MPa)      3      4                                                 T.sub.B (MPa)        20     17                                                E.sub.B (%)          450    400                                               ______________________________________                                    

The control sample, A, is a representative commercial polychloropreneelastomer formulation. Both samples processed well providing smooth,rubbery homogeneous-appearing slabs and test pieces. When the TFE resinwas mill mixed into the polychloroprene elastomer, during preparation ofsample B, there was no visible agglomeration of the TFE resin. The resinwas dispersed as distinct particles and as plate-like aggregates ofdistinct particles, with no apparent fibrillation. Comparison of sampleB with the control, A, shows that the TFE resin provides a significantimprovement in tear strength.

EXAMPLE 21 Addition of Modified PTFE to SBR Elastomer

The TFE copolymer resin of Example 8 was mixed into a commerciallyavailable, 50 Mooney viscosity SBR 1500 elastomer along with filler andcuratives, on a two-roll rubber mill at a shear rate of about 100 sec⁻¹for ten minutes according to the following recipe.

    ______________________________________                                                         Parts                                                        Sample             A(Control)                                                                              B                                                ______________________________________                                        SBR 1500           100       100                                              TFE Copolymer Ex. 8                                                                              --        30                                               HAF Black          50        50                                               Stearic Acid       2         2                                                Zinc Oxide         5         5                                                Sulfur             2         2                                                2-Mercaptobenzothiazole                                                                          1.5       1.5                                              Copper Dimethyldithiocarbamate                                                                   0.1       0.1                                              ______________________________________                                    

After mixing, sheets were formed and press-cured at 153° C. for 30minutes.

Samples were die cut and tested as in Example 15.

    ______________________________________                                        Sample             A(Control)                                                                              B                                                ______________________________________                                        Tested at 25° C.                                                       Tear Strength (kN/m)                                                                             5         8                                                M.sub.100 (MPa)    3         5                                                T.sub.B (MPa)      23        21                                               E.sub.B (%)        350       350                                              ______________________________________                                    

The control sample, A, is a representative commercial SBR elastomerformulation. Both samples processed well providing smooth, rubberyhomogeneous-appearing slabs and test pieces. When the TFE resin was millmixed into the SBR elastomer, during preparation of sample B, there wasno visible agglomeration of the TFE resin. The resin was dispersed asdistinct particles and as plate-like aggregates of distinct particles,with no apparent fibrillation. Comparison of sample B with the control,A, shows that TFE resin provides a significant improvement in tearstrength.

EXAMPLE 22

Samples of the above TFE copolymer resin of Example 8 were mixed with a55.4/44.2/0.4 TFE/PMVE/VF2 copolymer(tetrafluoroethylene/perfluoro(methylvinyl-ether)/vinylidene fluoride),fillers and curatives on a two roll rubber mill at 100° C. and at ashear strain rate of 100 sec⁻¹ for 10 minutes according to the followingrecipe:

    ______________________________________                                                         Parts                                                        Sample             A(Control)                                                                              B                                                ______________________________________                                        TFE/PMVE/VF2 Copolymer                                                                           100       100                                              TFE Copolymer Ex. 8                                                                              none      30                                               Carbon Black (SAF) 10        10                                               PbO                4         4                                                K2AF*              3         3                                                Dicyclohexyl-18-Crown 6                                                                          4         4                                                ______________________________________                                         *Dipotassium salt of Bisphenol AF.                                       

After mixing, sheets were formed and press cured at 177° C. for 30minutes, and post cured for two days under nitrogen at 288° C.

Testing

Samples were die cut from the cured sheet and tested at 25° C. for tearstrength according to ASTM method D 470 and for tensile strengthaccording to ASTM method D 412. Measurements were made both in thedirection of mill rotation and transverse direction and then averaged.

    ______________________________________                                                         Parts                                                        Sample             A(Control)                                                                              B                                                ______________________________________                                        Tested at 25° C.                                                       Tear Strength (kN/m)                                                                             3.7       12                                               M.sub.100 (MPa)    10        14                                               T.sub.B (MPa)      22        14                                               E.sub.B (%)        150       100                                              ______________________________________                                         M.sub.100 = Modulus at 100% elongation.                                       T.sub.B = Tensile strength.                                                   E.sub.B = Elongation at break.                                           

All blends processed well providing smooth, rubberyhomogeneous-appearing slabs and test pieces. When the TFE copolymer wasmill mixed into the TFE/PMVE/VF2 copolymer, during preparation of sampleB, there was no agglomeration of the TFE copolymer. Examination of testpieces, prior to addition of black and curatives, using an opticalmicroscope showed the TFE copolymer to be uniformly dispersed with noevidence of fibrillation. Plate-like aggregates of size 10×5×2 μmcomposed of distinct particles were observed. Comparison of sample Bwith the control A shows that the TFE copolymer provides a significantimprovement in tear strength at 25° C. with no agglomeration intovisible clumps or nodes.

EXAMPLE 23 Drip Suppressant

A sample of the TFE copolymer resin prepared in Example 8 was mixed, ata level of 5%, into a commercially available ETFE copolymer(ethylene/tetrafluoroethylene copolymer having 2.2 weight percentperfluorobutyl ethylene units and a melt viscosity of 1×10⁴ poise at297° C.) at 280° C., using a Brabender Plastograph Mixer. There was novisible agglomeration or fibrillation of the TFE copolymer of Example 8.Electron photomicrographs showed that the TFE copolymer was uniformlydispersed as distinct particles or as plate-like aggregates of distinctparticles of dimension 10×5×2 μm or smaller. No fibrillation of the TFEcopolymer could be seen.

The above composition containing 5% TFE copolymer of Example 8, as wellas a control of the ETFE copolymer, was compression molded into testbars 10 cm ×1 cm ×0.25 cm. When these test bars were held vertically inthe open flame of a Bunsen Burner, it was observed that the compositioncontaining the TFE copolymer charred, with no melting or dripping;whereas the ETFE control melted and readily dripped into the flame. Thisshows that the TFE resin acts as an effective drip suppressant, even inthe absence of fibrillation of the TFE resin.

EXAMPLE 24 Increased Processing Rate

A sample of the TFE copolymer resin prepared in Example 8 was mixed, ata level of 1%, into a commercially available TFE/HFP copolymercontaining 12.3 weight percent HFP and having a melt flow number (ASTM D1238-70) of 6.8, at 370° C. using a W&P 28 mm twin-screw extruder. Therewas no visible agglomeration or fibrillation of the PTFE resin. Theabove composition, containing 1% of the TFE copolymer, as well as acontrol of TFE/HFP copolymer, were extrusion coated onto AWG 22 copperwire at a thickness of 0.1 mm. It was observed that the compositioncontaining the TFE copolymer of Example 8 could be extrusion coated ontothe wire at a line speed of 400 m/min, at a draw-down ratio of 80:1,whereas the TFE/HFP control could be coated at a line speed of only250m/min, at a draw-down ratio of 80:1, due to cone breakage at higherspeeds. From this, it can be seen that the TFE copolymer resin improvesthe extrusion speeds, even though fibrillation of the TFE resin does notoccur.

EXAMPLE 25

Tetrafluoroethylene copolymers prepared as described in Examples 4, 9and 11 were each blended into respective samples of a 45 MooneyViscosity VF2/HFP 60:40 (weight ratio) copolymer, along with fillers andcuratives, on a two-roll rubber mill at a shear strain rate of about 100sec⁻¹ for 10 minutes, according to the following recipe:

    ______________________________________                                                      Parts                                                           Sample          A      B        C    Control                                  ______________________________________                                        VF2/HFP copolymer                                                                             100    100      100  100                                      TFE copolymer Ex. 9                                                                           43     --       --   --                                       TFE copolymer Ex. 4                                                                           --     43       --   --                                       TFE copolymer Ex. 11                                                                          --     --       43   --                                       MT Black        5      5        5    5                                        Ca(OH).sub.2    6      6        6    6                                        MgO             3      3        3    3                                        Additive 1.sup.1                                                                              1.28   1.28     1.28 1.28                                     Additive 2.sup.2                                                                              2.8    2.8      2.8  2.8                                      ______________________________________                                         .sup.1 A 2.1 blend of a VF2/HFP copolymer with benzyltriphenylphosphonium     chloride.                                                                     .sup.2 A 48:50:2 blend of a VF2/HFP copolymer with Bisphenol AF and rice      bran wax.                                                                

All samples processed well, providing smooth, rubberyhomogeneous-appearing sheets. When the TFE copolymer resins were millmixed into the respective VF2/HFP copolymer samples, there was noagglomeration of the TFE copolymer. Examination of the compositionsusing an optical microscope showed the TFE copolymer to be uniformlydispersed in the copolymer as distinct particles with no evidence ofagglomeration or fibrillation. Plate-like aggregates of size 10×5×2 μm,composed of distinct particles, were observed. After mixing, sheets wereformed and press-cured at 177° C. for 15 minutes, then post cured at232° C. for 24 hours.

The samples were die cut from the cured sheet and tested for tearstrength at room temperature according to ASTM method D 470 and fortensile properties at room temperature according to ASTM method D 412.Measurements were made both in the direction of mill rotation andtransverse direction and then averaged.

    ______________________________________                                                      Sample                                                                        A    B        C      Control                                    ______________________________________                                        Tested at 25° C.                                                       Tear Strength (kN/m)                                                                          7      6        10   5                                        M.sub.100 (MPa) 4      4        7    3                                        T.sub.B (MPa)   9      9        20   9                                        E.sub.B (%)     312    318      280  368                                      ______________________________________                                         M.sub.100 = Modulus at 100% elongation                                        T.sub.B = Tensile Strength                                                    E.sub.B = Elongation at Break                                            

Comparison of samples A, B, C and the control shows that the modifiedPTFE resins provide a significant degree of reinforcement andimprovement in tear strength at 25° C. with no fibrillation oragglomeration into visible clumps or nodes.

We claim:
 1. Blend of(a) an elastomeric resin, and (b) 0.1 to 200 partsper 100 parts of component (a) of a dispersion-process-produced,non-melt-processible, particulate, core-shell, tetrafluoroethylenecopolymer, the copolymer being present in said resin in the form ofplatelets distributed throughout the resin and comprising recurringunits of tetrafluoroethylene and modifying recurring units of acomonomer selected from the class consisting of hexafluoropropylene,perfluoro(alkyl vinyl ethers), perfluoro(alkyl vinyl ethers) wherein analkyl group is replaced with a hexafluoropropylene oxide oligomer,chlorotrifluoroethylene, and a mixture thereof, the number of recurringunits of comonomer in the shell being sufficient to enable the copolymerto compound uniformly with said resin without forming visibleagglomerates.
 2. The blend of claim 1 wherein component (a) is anelastomeric resin and component (b) is present in an amount of 1-200parts per 100 parts of elastomeric resin.
 3. The blend of claim 1wherein the comonomer of the tetrafluoroethylene copolymer is selectedfrom the class consisting of hexafluoropropylene, perfluoro(alkyl vinylethers), and a mixture of them.
 4. The blend of claim 3 wherein thealkyl group of the perfluoro(alkyl vinyl ether) contains 1-4 carbonatoms.
 5. The blend of claim 1 wherein the tetrafluoroethylene copolymeris comprised of at least 0.08 weight percent of recurring units ofhexafluoropropylene.
 6. The blend of claim 1 wherein thetetrafluoroethylene copolymer is comprised of greater than 0.02 weightpercent of recurring units of a perfluoro(alkyl vinyl ether).
 7. Theblend of claim 1 containing a filler.
 8. The blend of claim 1 containinga curing agent.
 9. Cured blend of claim
 8. 10. Blend of claim 2 whereinthe elastomer is a vinylidene fluoride/hexafluoroproplylene copolymer.11. Blend of claim 2 wherein the elastomer is a vinylidenefluoride/hexafluoropropylene/tetrafluoroethylene copolymer.
 12. Blend ofclaim 2 wherein the elastomer is a fluorosilicone elastomer.
 13. Blendof claim 2 wherein the elastomer is an ethylene/propylene/dienecopolymer.
 14. Blend of claim 2 wherein the elastomer is apolychloroprene.
 15. Blend of claim 2 wherein the elastomer is astyrene/butadiene copolymer.
 16. Blend of claim 2 wherein the elastomeris a tetrafluoroethylene/perfluoro(methyl vinyl ether) copolymer. 17.Blend of claim 2 wherein the elastomer is atetrafluoroethylene/perfluoro(methyl vinyl ether)/vinylidene fluoridecopolymer.